The present invention relates to detection of malfunction during intravascular delivery of fluids and, in particular, it concerns a method and device for detecting extravasation.
A common problem encountered in intravenous fluid administration is the infiltration of the fluids into tissues near the tip of the catheter. This phenomenon, variously referred to as xe2x80x9cinfiltrationxe2x80x9d and xe2x80x9cextravasationxe2x80x9d, may occur through a number of different mechanisms, not all of which are completely understood, but is often due to patient movement and disruption of the vein or artery at the end of the catheter. Although some texts make certain distinctions between the terms infiltration and extravasation, they are widely used, and will be used herein, interchangeably to denote generically any and all circumstances in which intravenous fluid delivery spreads beyond the blood vessel to adjacent tissue. Extravasation may lead to discoloration, discomfort and tissue destruction as well as lack of delivery of the intravenous fluids or drugs into the patient""s system. In the case of certain medications, infiltration of the drugs into the patient""s tissues may be dangerous, causing necrosis or other serious damage, requiring surgical procedures such as amputation. Permanent disfigurement and/or disability may result.
A number of devices and methods have been proposed for detection of tissue infiltration during intravenous administration of fluids. A common method for detecting infiltration is by monitoring the rate of flow or pressure of fluid in the supply line. Examples of such devices are disclosed in U.S. Pat. No. 4,534,756 to Nelson, U.S. Pat. No. 4,784,648 to Singh et al., and U.S. Pat. No. 4,979,940 to Bobo, Jr. et al. Commercially available devices based on these techniques, however, are generally ineffective since the pressure differences indicative of extravasation are typically small in relation to other causes of pressure variations such as patient movements or changes in the head pressure of an infusion bag.
A second approach to detection of extravasation is based upon the measurement of the skin temperature in potential infiltration areas. These devices use temperature sensors for continuous monitoring of the skin temperature near the intravenous catheter. When colder intravenous fluids accumulate in tissue from infiltration the skin temperature falls. Examples of such devices may be found in U.S. Pat. No. 4,010,749 to Shaw and U.S. Pat. No. 4,378,808 to Lichtenstein. These devices do not work well when the administered fluid is not significantly colder than the patient""s skin, when slow delivery rates are used, or when the patient""s body temperature varies. Such devices are also highly susceptible to false alarms due to changes in ambient temperatures.
Additional examples of proposed techniques include measurements of conductivity (e.g. U.S. Pat. No. 5,964,703 to Goodman et al.) and measurements of spectral reflection (e.g. U.S. Pat. No. 4,877,034 to Atkins et al.).
Due to the cost and reliability limitations of the available devices, the predominant technique for identifying extravasation remains visual inspection by hospital personnel of the area surrounding the catheter for swelling or other signs of infiltration. To be effective this technique requires continual monitoring by trained hospital personnel.
There is therefore a need for a device and method for detecting extravasation of fluid into tissue surrounding a blood vessel into which the fluid is intended to be delivered.
The present invention is a method and device for detecting extravasation.
According to the teachings of the present invention there is provided, a method for detecting extravasation of a fluid delivered from the tip of a catheter into tissue located under a first region of skin, the method comprising: (a) deploying on the skin a sensor system including: (i) a first sensor including a layer of piezoelectric film disposed in thermal and mechanical connection with the first region of skin, the first sensor providing a sensing signal, (ii) a second sensor including a layer of piezoelectric film disposed in mechanical connection with, but thermally isolated from, a second region of skin, the second sensor providing a reference signal, and (iii) a third sensor including a layer of piezoelectric film disposed in mechanical connection with, but thermally isolated from, a third region of skin, the third sensor providing a gate signal; (b) subtracting the reference signal from the sensing signal to generate a corrected sensing signal and from the gate signal to generate a corrected gate signal; (c) when an amplitude of the corrected gate signal is no greater than a predefined gate threshold value, monitoring the corrected sensing signal to detect at least one variation indicative of a malfunction, and (d) when an amplitude of the corrected gate signal is greater than the predefined gate threshold value, temporarily disregarding variations in the corrected sensing signal.
According to a further feature of the present invention, the at least one variation indicative of a malfunction includes a sequence of two variations occurring between 0.1 seconds and 100 seconds apart.
According to a further feature of the present invention, the at least one variation indicative of a malfunction includes a sequence of two variations occurring between 0.5 seconds and 10 seconds apart.
There is also provided according to the teachings of the present invention, a method for detecting extravasation of a fluid delivered from the tip of a catheter into tissue located under a first region of skin, the method comprising: (a) deploying on the skin a non-invasive sensor system including at least one sensor producing at least one output, the sensor system being operative to identify changes in both subcutaneous interstitial fluid pressure in the first region of skin and a skin temperature; (b) monitoring the at least one output to identify a sequence of variations in the at least one output corresponding to a skin temperature drop followed by a interstitial fluid pressure increase; and (c) generating an alarm condition when the sequence of variations occurs.
According to a further feature of the present invention, the at least one sensor includes at least one measuring sensor and a gate sensor, the gate sensor producing an output indicative of disruptive motion likely to adversely affect an output of the at least one measuring sensor, the method further comprising disregarding the output of the at least one measuring sensor when the output of the gate sensor indicates the occurrence of disruptive motion.
According to a further feature of the present invention, the at least one sensor includes a piezoelectric film primary sensor sensitive simultaneously to variations in interstitial fluid pressure and skin temperature.
According to a further feature of the present invention, the sensor system further includes a piezoelectric film reference sensor insulated so as to be unaffected by variations in the skin temperature, an output from the reference sensor being subtracted from an output from the primary sensor.
There is also provided according to the teachings of the present invention, a system for detecting extravasation of a fluid delivered from the tip of a catheter into tissue located under a first region of skin, the system comprising: (a) a sensor system for non-invasive deployment on the skin, the sensor system including: (i) a first sensor including a layer of piezoelectric film configured to be disposed in thermal and mechanical connection with the first region of skin, the first sensor providing a sensing signal, (ii) a second sensor including a layer of piezoelectric film configured to be disposed in mechanical connection with, but thermally isolated from, a second region of skin, the second sensor providing a reference signal, and (iii) a third sensor including a layer of piezoelectric film configured to be disposed in mechanical connection with, but thermally isolated from, a third region of skin, the third sensor providing a gate signal; and (b) a processing system electrically coupled to the first second and third sensors, the processing system including: (i) a first differencing module configured to subtract the reference signal from the sensing signal to generate a corrected sensing signal, (ii) a second differencing module configured to subtract the reference signal from the gate signal to generate a corrected gate signal, (iii) a comparator module configured to compare a current amplitude of the corrected gate signal with a predefined gate threshold value, and (iv) a monitoring module configured to monitor the corrected sensing signal during periods when the comparator module determines that the corrected gate signal is no greater than the threshold value to detect at least one variation in the corrected sensing signal indicative of a malfunction.
According to a further feature of the present invention, there is also provided a closure device associated with the processing system and with a conduit supplying the fluid to the catheter, the closure device being responsive to the monitoring module to prevent fluid flow through the conduit when the at least one variation in the corrected sensing signal is indicative of a malfunction.